(i) Field of the Invention
The present invention relates to a process and to a device for supplying gas to an analyzer of traces of impurities in a gas and, more particularly, to such a process and to such a device, according to which the analyzer is supplied sequentially with a gas to be analyzed, a pure gas and a standardizing gas obtained by dilution of one or more impurities in this pure gas.
(ii) Description of the Related Art
Such a process and such a device, designed for feeding an analyzer of very high sensitivity are known from document FR-A-2 667 397 in the Applicant's name. Such an analyzer can be designed to detect impurities in very low concentrations (for example 10.sup.-2 -10.sup.-5 ppm). It must then be frequently standardized by supplying a pure or "zero" gas and a "standardizing" gas containing impurities in accurately determined concentrations.
In the device of the abovementioned document a constant gas flow is ensured in each of the lines supplying to the analyzer the gas to be analyzed, a pure gas and a standardizing gas charged with a predetermined quantity of impurities, respectively, by arranging in each line a calibrated orifice operating in the sonic regime and a pressure sensor upstream of this orifice, the sensed pressure control-driving a flow regulator placed in a discharge bypass of the line, downstream of the orifice. To prevent the pressure sensor from contaminating the gas traveling in the line, the sensor is fitted in a bypass equipped with a leakage line permitting a small leakage flow in this bypass. All these precautions increase the bulk of the device as well as its complexity and its cost of manufacture. The bulkiness of the device is further burdened by the use of a bottle filled with standardizing gas. Furthermore, the accuracy of flow regulation is affected by that of the pressure measurement performed by the sensor, which itself must be corrected for temperature when the latter varies.